<template>
  <view class="u-wrap">
    <view class="u-search-box">
      <view class="u-search-inner">
        <u-icon name="search" color="#909399" :size="28"></u-icon>
        <text class="u-search-text">搜索</text>
      </view>
    </view>
    <view class="u-menu-wrap">
      <scroll-view scroll-y scroll-with-animation class="u-tab-view menu-scroll-view" :scroll-top="scrollTop"
        :scroll-into-view="itemId">
        <view v-for="(item,index) in tabbar" :key="index" class="u-tab-item" :class="[current == index ? 'u-tab-item-active' : '']"
          @tap.stop="swichMenu(index)">
          <text class="u-line-1">{{item.name}}</text>
        </view>
      </scroll-view>
      <scroll-view :scroll-top="scrollRightTop" scroll-y scroll-with-animation class="right-box" @scroll="rightScroll">
        <view class="page-view">
          <view class="class-item" :id="'item' + index" v-for="(item , index) in tabbar" :key="index">
            <view class="item-title">
              <text>{{item.name}}</text>
            </view>
            <view class="item-container">
              <view class="thumb-box" v-for="(item1, index1) in item.foods" :key="index1">
                <image class="item-menu-image" :src="item1.icon" mode=""></image>
                <view class="item-menu-name">{{item1.name}}</view>
              </view>
            </view>
          </view>
        </view>
      </scroll-view>
    </view>
  </view>
</template>
<script>
  import classifyData from '@/common/classify.data.js';
  export default {
    data() {
      return {
        scrollTop: 0, //tab标题的滚动条位置
        oldScrollTop: 0,
        current: 0, // 预设当前项的值
        menuHeight: 0, // 左边菜单的高度
        menuItemHeight: 0, // 左边菜单item的高度
        itemId: '', // 栏目右边scroll-view用于滚动的id
        tabbar: classifyData,
        menuItemPos: [],
        arr: [],
        scrollRightTop: 0, // 右边栏目scroll-view的滚动条高度
        timer: null, // 定时器

      }
    },
    onLoad() {

    },
    onReady() {
      this.getMenuItemTop()
    },
    methods: {
      // 点击左边的栏目切换
      async swichMenu(index) {
        if (this.arr.length == 0) {
          await this.getMenuItemTop();
        }
        if (index == this.current) return;
        this.scrollRightTop = this.oldScrollTop;
        this.$nextTick(function() {
          this.scrollRightTop = this.arr[index];
          this.current = index;
          this.leftMenuStatus(index);
        })
      },
      // 获取一个目标元素的高度
      getElRect(elClass, dataVal) {
        new Promise((resolve, reject) => {
          const query = uni.createSelectorQuery().in(this);
          query.select('.' + elClass).fields({
            size: true
          }, res => {
            // 如果节点尚未生成，res值为null，循环调用执行
            if (!res) {
              setTimeout(() => {
                this.getElRect(elClass);
              }, 10);
              return;
            }
            this[dataVal] = res.height;
            resolve();
          }).exec();
        })
      },
      // 观测元素相交状态
      async observer() {
        this.tabbar.map((val, index) => {
          let observer = uni.createIntersectionObserver(this);
          // 检测右边scroll-view的id为itemxx的元素与right-box的相交状态
          // 如果跟.right-box底部相交，就动态设置左边栏目的活动状态
          observer.relativeTo('.right-box', {
            top: 0
          }).observe('#item' + index, res => {
            if (res.intersectionRatio > 0) {
              let id = res.id.substring(4);
              this.leftMenuStatus(id);
            }
          })
        })
      },
      // 设置左边菜单的滚动状态
      async leftMenuStatus(index) {
        this.current = index;
        // 如果为0，意味着尚未初始化
        if (this.menuHeight == 0 || this.menuItemHeight == 0) {
          await this.getElRect('menu-scroll-view', 'menuHeight');
          await this.getElRect('u-tab-item', 'menuItemHeight');
        }
        // 将菜单活动item垂直居中
        this.scrollTop = index * this.menuItemHeight + this.menuItemHeight / 2 - this.menuHeight / 2;
      },
      // 获取右边菜单每个item到顶部的距离
      getMenuItemTop() {
        new Promise(resolve => {
          let selectorQuery = uni.createSelectorQuery();
          selectorQuery.selectAll('.class-item').boundingClientRect((rects) => {
            // 如果节点尚未生成，rects值为[](因为用selectAll，所以返回的是数组)，循环调用执行
            if (!rects.length) {
              setTimeout(() => {
                this.getMenuItemTop();
              }, 10);
              return;
            }
            rects.forEach((rect) => {
              // 这里减去rects[0].top，是因为第一项顶部可能不是贴到导航栏(比如有个搜索框的情况)
              this.arr.push(rect.top - rects[0].top);
              resolve();
            })
          }).exec()
        })
      },
      // 右边菜单滚动
      async rightScroll(e) {
        this.oldScrollTop = e.detail.scrollTop;
        if (this.arr.length == 0) {
          await this.getMenuItemTop();
        }
        if (this.timer) return;
        if (!this.menuHeight) {
          await this.getElRect('menu-scroll-view', 'menuHeight');
        }
        setTimeout(() => { // 节流
          this.timer = null;
          // scrollHeight为右边菜单垂直中点位置
          let scrollHeight = e.detail.scrollTop + this.menuHeight / 2;
          for (let i = 0; i < this.arr.length; i++) {
            let height1 = this.arr[i];
            let height2 = this.arr[i + 1];
            // 如果不存在height2，意味着数据循环已经到了最后一个，设置左边菜单为最后一项即可
            if (!height2 || scrollHeight >= height1 && scrollHeight < height2) {
              this.leftMenuStatus(i);
              return;
            }
          }
        }, 10)
      }
    }
  }
</script>

<style lang="scss" scoped>
  .u-wrap {
    height: calc(100vh);
    /* #ifdef H5 */
    height: calc(100vh - var(--window-top));
    /* #endif */
    display: flex;
    flex-direction: column;
  }

  .u-search-box {
    padding: 18rpx 30rpx;
  }

  .u-menu-wrap {
    flex: 1;
    display: flex;
    overflow: hidden;
  }

  .u-search-inner {
    background-color: rgb(234, 234, 234);
    border-radius: 100rpx;
    display: flex;
    align-items: center;
    padding: 10rpx 16rpx;
  }

  .u-search-text {
    font-size: 26rpx;
    color: $u-tips-color;
    margin-left: 10rpx;
  }

  .u-tab-view {
    width: 200rpx;
    height: 100%;
    background: #f6f6f6;
  }

  .u-tab-item {
    height: 110rpx;
    box-sizing: border-box;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 26rpx;
    color: #444;
    font-weight: 400;
    line-height: 1;
  }

  .u-tab-item-active {
    position: relative;
    color: #000;
    font-size: 30rpx;
    font-weight: 600;
    background: #fff;
    border-radius: 15rpx;

    &:before {
      content: "";
      position: absolute;
      border-left: 4px solid $base-color-default;
      height: 32rpx;
      left: 0;
      top: 39rpx;
    }
  }


  .u-tab-view {
    height: 100%;
  }

  .right-box {
    background-color: rgb(250, 250, 250);
  }

  .page-view {
    padding: 16rpx;
  }

  .class-item {
    margin-bottom: 30rpx;
    background-color: #fff;
    padding: 16rpx;
    border-radius: 8rpx;
  }

  .class-item:last-child {
    min-height: 100vh;
  }

  .item-title {
    font-size: 26rpx;
    color: $u-main-color;
    font-weight: bold;
  }

  .item-menu-name {
    font-weight: normal;
    font-size: 24rpx;
    color: $u-main-color;
  }

  .item-container {
    display: flex;
    flex-wrap: wrap;
  }

  .thumb-box {
    width: 33.333333%;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    margin-top: 20rpx;
  }

  .item-menu-image {
    width: 120rpx;
    height: 120rpx;
  }
</style>
